The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Firearm projectiles used for hunting are generally small caliber, e.g., less than 0.50 caliber. Firearm projectiles commonly have a hollow point or soft metal nose portion to increase expansion of the projectile upon impact with animal tissue in order to achieve increased energy adsorption within the target animal's body. Many hunting projectiles, specifically lead-tipped or hollow point projectiles, have a significant drawback for use in hunting applications in that the projectiles tend to upset and expand greatly (even to the point of fragmentation), thus expending most of their energy and penetrating only a short distance. Accordingly, such projectiles are thus not particularly suitable for deep penetration. This is particularly true where the projectile hits a bone during passage into the animal. Hunters often aim for the shoulder area of the target animal in order to minimize (or at least reduce) the chance of the animal escaping after it has been shot. Plus, the animal's vital organs are usually in the same general area of the animal as the shoulder. As a result, it is not uncommon for the projectile to strike bone.
Projectile expansion is generally desirable for hunting to slow the projectile such that more energy is transferred to the target during passage through soft animal tissue. If the projectile does not expand significantly and does not hit a bone or vital organ, the projectile may pass through the animal without killing or stopping the animal. For the projectile to successfully pass through animal bone and still do damage to vital organs, it is usually necessary that the projectile have sufficient density, sufficient structural integrity, and retained weight.
Firearm projectiles used for hunting applications sometimes include unitary metal bodies with generally H-shaped longitudinal cross sections with an empty hollow point in front, and a rear cavity filled with a dense core formed from a material, such as lead. The rear cavity may be closed by a disk to seal the dense core from the environment. Because the rear cavity is filled with a dense core, the majority of the weight of this projectile is contained in the rear portion. As a result, this projectile has good weight retention because the projectile does not lose a significant part of its weight even when the petals in the front break off during penetration of the target.
This example projectile tends to bulge due to the forward inertia and kinetic energy of the heavy dense core during the rapid deceleration upon impact. Specifically, the forward portion of the sidewalls of the rear cavity of the projectile tends to bulge. This can be advantageous in that the bulge can help make a larger diameter wound channel. But the dense core of this projectile is not bonded to the sidewalls of the rear cavity. Rather, the dense core is pressure fit within the rear cavity. As a result, this projectile has been found to break apart when it hits heavy bones at or near muzzle velocity. Failure has been found to develop at the bulge portion. When the projectile breaks apart, the dense core is separated from the jacket, thereby undermining overall performance. In addition, because many dense cores contain lead, it is generally desired that the integrity of the projectile be maintained to prevent (or at least reduce) contamination of animal tissue due to lead exposure.